Clojure

thread-bound? returns true (implying set! should succeed) even for non-binding thread

Details

  • Type: Defect Defect
  • Status: Open Open
  • Priority: Major Major
  • Resolution: Unresolved
  • Affects Version/s: None
  • Fix Version/s: None
  • Component/s: None
  • Labels:
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  • Patch:
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Description

thread-bound? returns true for a non-binding thread, this result (according to the docstring) implies that set! should succeed. However, thread-bound? does not check that any binding that might exist was created by the current thread, and calling set! fails with an exception when it is called from a non-binding thread, even though thread-bound? returns true.

thread-bound? should return false if there is a binding, and that binding was not established by the current thread.

Here is an example REPL session where a thread establishes a binding, those bindings are conveyed to a second thread, the second thread checks thread-bound? to see if it can set the binding, thread-bound? returns true indicating that the binding can be set, the second thread tries to set the binding, and the second thread gets an IllegalStateException:

    Clojure 1.5.1
    user=> (def ^:dynamic *set-me* nil)
    #'user/*set-me*
    user=> (defn try-to-set [] (binding [*set-me* 1] (doall (pcalls #(if (thread-bound? #'*set-me*) (set! *set-me* (inc *set-me*)))))))
    #'user/try-to-set
    user=> (try-to-set)
    IllegalStateException Can't set!: *set-me* from non-binding thread  clojure.lang.Var.set (Var.java:230)
    user=> 

Activity

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Joe Gallo added a comment -

Sure thing, Alex – here's a repl example I just ran this morning.

; nREPL 0.1.7
user> (def ^:dynamic *set-me* nil)
#'user/*set-me*
user> (defn try-to-set [] (binding [*set-me* 1] (doall (pcalls #(if (thread-bound? #'*set-me*) (set! *set-me* (inc *set-me*)))))))
#'user/try-to-set
user> (try-to-set)
IllegalStateException Can't set!: *set-me* from non-binding thread  clojure.lang.Var.set (Var.java:230)
user>
Show
Joe Gallo added a comment - Sure thing, Alex – here's a repl example I just ran this morning.
; nREPL 0.1.7
user> (def ^:dynamic *set-me* nil)
#'user/*set-me*
user> (defn try-to-set [] (binding [*set-me* 1] (doall (pcalls #(if (thread-bound? #'*set-me*) (set! *set-me* (inc *set-me*)))))))
#'user/try-to-set
user> (try-to-set)
IllegalStateException Can't set!: *set-me* from non-binding thread  clojure.lang.Var.set (Var.java:230)
user>
Hide
Alex Miller added a comment -

REPL example?

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Alex Miller added a comment - REPL example?
Hide
Paul Stadig added a comment - - edited

I have attached a patch that changes clojure.lang.Var and clojure.core/thread-bound? to only return true if a Var is set!-able.

Show
Paul Stadig added a comment - - edited I have attached a patch that changes clojure.lang.Var and clojure.core/thread-bound? to only return true if a Var is set!-able.

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  • Created:
    Updated: